(1) Field of the Invention
The present invention relates to a process for the preparation of an anti-fogging coating capable of imparting a highly durable anti-fogging property.
The present invention is especially suitable for the preparation of an anti-fogging coating on inorganic glass and plastic materials.
(2) Description of the Related Art
Plastic materials and inorganic glass materials are widely used for articles such as window-panes, mirrors, spectacle lenses and goggles, in view of their good properties as a transparent substrate. Nevertheless, when articles comprising these transparent substrates are used in high-temperature and high-humidity conditions or at a boundary surface where the difference of the temperature or humidity is large, dewing occurs on the surfaces of the articles and the surfaces of the articles become foggy. Especially in the case of transparent substrates such as windowpanes, spectacle lenses and mirrors, a serious problem exists in that the article surface becomes foggy or is easily damaged. Accordingly, means for eliminating such disadvantage are urgently required in various fields, and attempts have been made to impart an anti-fogging property and a durability to various articles represented by transparent substrates.
As the simplest method for manifesting an anti-fogging effect, a method has been proposed wherein the wettability of the surface of an article is improved by coating or incorporating a hydrophilic substance such as a surface active agent (see, for example, U.S. Pat. No. 3,479,308). According to this method, however, only temporary anti-fogging property is given to an article and a durable effect cannot be obtained.
Coating of polyvinyl alcohol or other hydrophilic polymers for imparting a durable anti-fogging property has been proposed. For example, U.S. Pat. No. 4,127,682 proposes an anti-fogging agent comprising a polyvinyl alcohol crosslinked with zirconium nitrate and formaldehyde.
Furthermore, it is known that a polyvinyl alcohol is crosslinked with finely divided silica to give a water-resistant coating (see U.S. Pat. No. 3,773,776).
Moreover, a curable coating composition comprising a polyvinyl alcohol/silica complex as the main component is proposed (see U.S. Pat. No. 4,016,129).
Nevertheless, according to these proposals, the hydrophilic characteristics of the polyvinyl alcohol are drastically reduced. Namely, the anti-fogging property of the polyvinyl alcohol becomes very poor, and satisfactory anti-fogging coating materials cannot be provided.
Still further, a technique of forming a two-layer coating composed of a polyvinyl alcohol, finely divided silica and an organic silicon compound has been proposed (see U.S. Pat. No. 4,478,909), but this technique does not give a sufficient anti-fogging property.